“It requires an examination and comparison of the building as it was or (if more than one) the buildings as they were before the works were carried out and the building or buildings as they will be after the works are completed; and the question then to be asked is whether the completed works amount to the enlargement of or the construction of an extension or annexe to the original building (see Customs and Excise Comrs v Marchday Holdings Ltd[1997] STC 272 at 279). I must however add a few words regarding how the question is to be approached and answered. First the question is to be asked as at the date of the supply. What was in the course of construction at the date of supply is in any ordinary case (save for example in case of a dramatic change in the plans) the building subsequently constructed. Secondly the answer must be given after an objective examination of the physical characters of the building or buildings at the two points in time, having regard (inter alia) to similarities and differences in appearance, the layout and how the building or buildings are equipped to function. The terms of planning permissions, the motives behind undertaking the works and the intended or subsequent actual use are irrelevant, save possibly to illuminate the potentials for use inherent in the building or buildings.”
“… I see no reason to import the notion that the additional dwelling must be incorporated wholly within that enlargement or extension.”
“It is well established that, when considering Note (16) in its application to cases of this kind, it is necessary first to determine precisely what has been done. To do so, one should examine the original building and then the finished development and, by comparing the two, put oneself in a position to determine whether the result amounts to 'the conversion, reconstruction or alteration of [the] existing building', on the one hand, or the 'enlargement of, or extension to, [the] existing building', on the other; and if the answer is the latter, one must then move on to consider the proviso to paragraph (b) of the Note.”
“In my view, the natural meaning of the words used in Note (16) is that an enlargement or extension qualifies for zero-rating if it creates an additional dwelling.”